Communication systems respond to control signals in order to establish connections between terminals and, in turn, supply control signals to a user as a means of alerting the user as to the status of a connection. For example, a communication system user recognizes busy tone as an indication that a called terminal is not available. Control signals can either represent digits, such as rotary dial digits or multifrequency tone digits, or service signals such as busy tone or all paths busy tone.
In the stored program controlled business customer system call processing time is lost connecting a multifrequency generator to a line for the purpose of applying either call progress or call alerting tones to a line. Typically, time is consumed establishing a connection between the line and the selected port of the multifrequency generator. The time consumed in establishing a connection during period of few calls presents no problem, however, during busy hours the accummulation of lost time becomes appreciable. Moreover, this problem is aggravated when the demand for multifrequency tones exceeds the capacity of the tone generator. A viable but expensive solution to the problem is to provide a sufficient number of multi-tone generators to satisfy worst case call processing needs.
Further, a multi-tone generator or oscillator is typically arranged to provide only a fixed number of tones or frequencies. If future services or features require a new tone, then the generator would have to be modified to provide the additional tone.
Prior digital communication system attack the problem by distributing premixed MF tones during assigned time slots of a system time division bus to system port circuits. These prior tone distribution systems use 10 time slots to provide digit tones that are used for telephone number generation and also use 2 time slots for distributing the star (*) and gate (#) signals. Such systems, under control of the central processor, switch the trunk or port circuit through a sequence of time slots for telephone number and special services generation.
Such use of a time division bus is inefficient in its use of system time slots which, if not carrying tone signals, could be assigned to call processing. Further, if future requirements are needed for the permanent assignment of additional tones to particular time slots, the efficiency of the bus would be further degraded.
Accordingly, a need exists in the art for a tone distribution system which readily satisfies future growth and one which uses a minimum amount of time slots and call processing real time.